New Insights Into Application Relevant Properties of Cu²⁺-Doped Brushite Cements

Doping of brushite cements with metal ions can entail many positive effects on biological and physicochemical properties. Cu²⁺ ions are known to exhibit antibacterial properties and can additionally have different positive effects on cells as trace elements, whereas high Cu²⁺ concentrations are cytotoxic. For therapeutical applications of bone cement, a combination of good biocompatibility and sufficient mechanical properties is required. Therefore, the aim of this study was to investigate different physicochemical and biological aspects, relevant for application, of a brushite cement with Cu²⁺-doped β-tricalcium phosphate, monocalcium phosphate monohydrate and phytic acid as setting retarder. Additionally, the ion release was compared with a cement with citric acid as setting retarder. The investigated cements showed good injectability coefficients, as well as compressive strength values sufficient for application. Furthermore, no antibacterial effects were detected irrespective of the Cu²⁺ concentration or the bacterial strain. The cell experiments with eluate samples showed that the viability of MC3T3-E1 cells tended to decrease with increasing Cu²⁺ concentration in the cement. It is suggested that these biological responses are caused by the difference in the Cu²⁺ release from the hardened cement depending on the solvent medium. Furthermore, the cements showed a steady release of Cu²⁺ ions to a lesser extent in comparison with a cement with citric acid as setting retarder, where a burst release of Cu²⁺ was observed. In conclusion, despite the anticipated antibacterial effect of Cu²⁺-doped cements was lacking and mammalian cell viability was slightly affected, Cu²⁺-concentrations maintained the physicochemical properties as well as the compressive strength of cements and the slow ion release from cements produced with phytic acid is considered advantageous compared to citric acid-based formulations.